1. Field of the Invention
The present invention relates to a comprehensive method for manufacturing functional molecules that exhibit high affinity for a variety of target substances, and that are particularly applicable to a wide range of fields including drugs, drug delivery, biosensors, controlling levels of gene expression, overcoming diseases caused by gene abnormalities or elucidating the functions of proteins translated through those genes, developing catalysts comparable to enzymes and the like. In the present invention, when a specific interaction can occur between a substance and a molecule the substance is called a target substance and the molecule is called a functional molecule. Interaction here includes physical adsorption and chemical adsorption as well as antigen-antibody reactions and other biological interactions. Affinity can be present when a specific interaction can occur.
2. Description of the Related Art
The complete human genome is already known. As a result, the attention of scientists has shifted to the analysis of the gene products, the proteins. It is not an exaggeration to say that in protein analysis, actual analysis of a protein can only be achieved by obtaining a functional molecule with affinity for that protein.
However, an extremely wide variety of proteins are contained in cells, and the sequences of many of them are unknown. The most common means of obtaining a functional molecule having affinity for a specific protein or other target substance is to select an affinity antibody using the immune system of an animal. Because animals are used in this method, however, a large quantity of protein is required, along with extensive procedures and costs. Another drawback has been that an affinity antibody to a specific substance is not produced.
One means for resolving such problems is the aptamer method (also called the Selex method), which does not rely on living animals {see, for example, U.S. Pat. No. 5,475,096 (Claims)}, but this method produces strong interactions only with certain proteins, and is not applicable to all proteins. The modified aptamer method has also been developed which uses a modified nucleic acid as a functional molecule, but only unmodified nucleic acids are produced via PCR, so this does not permit multiple selections as in the Selex method, and one problem has been how to effectively exclude non-specific interactions from a system containing multiple kinds of modified nucleic acids.